One of the most serious problems in the handling of mail or envelopes is stacking. It is desirable to feed letters to a stack of letters, where the insertion of the envelopes is easily accomplished and the integrity of the stack of mail is properly maintained. With present equipment, letters are forced by rotating paddles or brushes into a stack of mail under compressive load. The load applied to the stack is necessary to maintain the integrity of the pieces of mail as a unit mass. However, this stack pressure causes the incoming pieces of mail to meet with a large frictional resistance. This often results in jamming. In order to overcome this resistance, paddles or rollers propelling the mail are made to rotate at higher speeds. The added speed, however, causes greater wear damage to the envelopes. Also, the higher speed imparts more energy to the envelopes, which causes them to bounce out of the stack.
Intermixed mail of different sizes and weight is particularly a problem. The fixed speeds of the paddles, and the fixed pressure of the stack cannot be automatically varied to accommodate large variations in the letter weight and size. Adjusted to light letters, the stacking system often tends to jam for heavier pieces of mail. Adjusted for heavier pieces, the lighter pieces often tend to bounce out of the stack.
The present invention seeks to eliminate the aforementioned problems by providing a self-clearing wide-angled inlet window for easy letter insertion. The stack of mail is held conveniently away from the inlet window and the rotating rollers, to prevent jamming and wear.